HVAC Selector Wiring

[bfisher]

Took me a couple days to get a spare few minutes to put this together, but you were right - 1-17 is 24V in heat, and 1-19 is 24V in Cool or Fan.

Unless I'm mistaken, now I need to figure out how to get 24VAC into a usable VDC so I can monitor on/off (my HVPro doesn't accept 24VAC).

 

[JKnox]

Sorry about the delay, somehow I missed your reply... :lol:

Anyway, it does look like you've found the correct points to monitor. But I wouldn't even think of trying to hook this to your Homevision without using some kind of isolation - that panel looks far too nice to risk taking it out with an errant surge (which are pretty common in a HVAC setup)!

That said, what are you comfortable building, and what stuff do you have available? The easiest method would be to use a 24VAC relay, but if you don't already have one they can be harder to find and a bit pricey to boot (at least when looking at a $10 mark).

An opto-based circuit would be my favorite. Easy enough for anybody with basic soldering skills to build, but for price it again depends on what you have available. The parts themselves are under $10, but if you've got to order the stuff, you bump into minimum order fees.

Anyway, the hard part is done. Let's get it talking to your panel!

Jerry

 

[bfisher]

No problem on the delay - I'm not in a rush since I want this working by Spring when I next need to change the switch :lol:

Personally, I'd like to make this for less than $20 (if possible). Cost isn't a big factor, but since this won't be used frequently (I think we change that switch maybe 5-10 times a year max, but probably really only 2-3 times). My goal in making it is to make it transparent so if I'm not home and my wife decides to change the switch from Fan to Heat (for example) - she doesn't need to know that the thermostats are not right. The switch will tell my HVPro to readjust the thermostats for HEAT mode.

I am pretty comfortable with soldering irons and basic wiring. I have an Engineering background but it's been so long since I've used it I can't remember enough details to design it myself. Plus I don't know where to buy components like these. So I definitely appreciate your help!!

 

[JKnox]

Just looked over your pictures. Wow.

There's now an additional requirement - it has to look decent!

One thing - do you just want to monitor heat? Or both heat and cool modes (which would let you determine 'off')? Or more?

With the opto method, it's only a tiny step to add another channel. The optos I like to use (Liteon LTV-8141) only require a single resistor and capacitor for this type of usage.

I have a dual channel one mocked up on a breadboard that is only 1.75" x 1.75" x .75" - and that board is larger than needed. Even with the screw terminals. I could make it 4 channel and still have enough space.

So it's easiest to think about any potential use while we're at it. For instance, it would be trivial at this stage to add another channel so you can monitor compressor runtime.

And I think I can make you a deal on parts (hey buddy, wanna buy an opto?).

Jerry

 

[bfisher]

I am very open about this project. My original plans were to keep it easy and just monitor heat. However, if it is just as easy to monitor other things (cool, compressor times, etc), I'd be happy to!

If you have some parts available that you don't need, I'm happy to buy them. If you need them, I can buy them elsewhere if you help me determine what I need.

I appreciate your assistance! I'm looking forward to getting this working

<edit: ps - thanks for the compliment about my cocoon >

 

[JKnox]

Looking at your zone controller pictures and combined with what we already know it looks like it would be trivially easy to monitor "heat/cool/off" mode along with separate heat and cool runtimes. Would take four channels of isolation.

From your other pictures it appears that you are using some of port B on the homevision. How many do you have left? Do you have any other ideas that might need inputs on ports B or C? What I would use would work fine with either port.

Jerry

p.s. You have a pm.

 

[bfisher]

After I finish my current plans, I will probably fill up the B Ports. The C ports are all available (5VDC Max I think). Some of the B Ports could be moved to C I think (based on their voltage capabilities) if we need more than 5 VDC.

 

[JKnox]

Port C will be fine - I was just curious mainly.

When using an opto-isolator design, the port's allowable voltage is pretty much a non-issue. To the controller, an opto basically looks like a normally-open contact switch.
The switch is closed when the monitored device is on.

Methinks I should write an Opto 101 topic. I've seen enough questions both here and on HS to warrant it. Might only take me a month...